With the advent of the CC-130(H)T (Hercules) aircraft in the role of air tanker in support
of the CF-18A fighter aircraft, a flight testing programme was initiated in order to establish the
compatibility of the two aircraft for Air-to-Air Refuelling (AAR). Concurrently, scale testing
was conducted in a low speed wind tunnel at the University of British Columbia to investigate
the effect of the CC-130H(T)'s wing-tip vortex on the CF-18A aircraft in the AAR pre-contact
position.
The scale testing was accomplished by subjecting a 1/12 scale model of the CF-18A to
the tip vortex of a generating wing placed upstream in a wind tunnel. Custom-designed mounts
allowed for variation of the model's vertical position and of the generating wing's lateral
position inside the wind tunnel. Force and pressure sensors installed on the model served to
measure the positional effects of the vortex for three AAR conditions defined by tanker vortex
strength and CF-18A angle-of-attack.
The present study has shown that, when considering the wing-tip vortex exclusively, the
optimal AAR pre-contact region is far inboard of and below the tanker wing tip, while the most
unstable region of the tip vortex is just outboard of and roughly level with the tanker's wing tip.
Furthermore, the magnitude of the aerodynamic forces on the model was observed to be
proportional to the strength of the generated vortex, and insignificant Reynolds number effects
were observed between half-speed and full-speed tests.